1. Field of the Invention
The present invention relates generally to satellite communication and navigation and, in particular, to an integrated navigation and communication system for use in distributed spacecraft systems.
2. Description of the Related Art
Distributed spacecraft systems (e.g., distributed satellite systems or spacecraft systems with some type of propulsion device) use multiple spacecraft to augment the capabilities of monolithic space system approaches. These systems, also referred to as formation flying systems, enable complex sensing tasks such as, for example, distributed aperture processing, co-observation, multipoint observation, and distributed interferometry, which are beyond the abilities of single spacecraft systems. Depending on the degree of inherent coordination, formation-flying systems differ from traditional satellite constellations in that the distributed system is treated as a whole, unified by common objectives. Both the National Aeronautics and Space Administration (NASA) and the Department of Defense (DoD) have identified distributed spacecraft system as a means to achieve mission goals in future deployments. NASA, for example, has identified campaigns of several space missions that largely rely on multiple spacecraft deployments. Operationally, however, such systems are in their infancy.
A significant number of Earth and space science goals rely on the successful deployment and operation of distributed spacecraft technology within future operational missions. In conjunction with fundamental science, distributed spacecraft military missions in support of defense operations have been identified as important capabilities to maintain national interests.
The specific advantages attributed to the use of distributed spacecraft systems include increased capability, gradual performance degradation in that failure of one of the spacecraft does not render the system obsolete, improved system robustness, and cost efficiency. Relative to single spacecraft systems, formation-flying systems provide improved capability by spatially disbursing sensors, thereby supporting extended and adaptive baselines for distributed sensing tasks. This approach also supports temporal sampling at variable resolutions and is a systematic mechanism for implementing space-based multi-sensor data fusion systems. Because capability is distributed among multiple spacecraft such as satellites, re-deploying functioning spacecraft can mitigate failures that impact individual spacecraft. Thus, while performance in terms of resolution or coverage of a target area may be reduced due to diminished spacecraft, basic functionality is retained. Compensating for failures in this manner allows distributed spacecraft systems to realize an improved level of robustness beyond that of a single spacecraft approach. Finally, the goal of cost-efficiency is embodied in the fact that such formation flying systems rely on the collective faculties of multiple, individually limited spacecraft. This often necessitates the use of small, economical spacecraft approaches that can be deployed in clusters to reduce launch costs.
Realizing the advantages of distributed spacecraft systems, however, entails considerable complexity in system design and implementation. It is not simply by virtue of the fact that multiple spacecrafts may be deployed that advantageous performance, capability, robustness, or cost efficiencies can be achieved. For coordinated formations, particularly autonomous or coherent distributed spacecraft systems, technologies and methodologies must provide mechanisms to support information exchange, coordination, autonomy, and dynamic adaptivity. The ability to realize such characteristics in a system must be greater than or commensurate with the level of coordination that is desired within the formation. For example, a loosely coupled, non-coherent system may only require crosslink communications to exchange state information or support health and status sharing among spacecraft. Alternatively, a coherent system designed to act as a distributed aperture (e.g., a virtual spacecraft with distributed elements) would require a considerably higher level of distributed control, precision navigation, precision differential timing, and high-rate crosslink communications for coordination and science data exchange.
Supporting collective systems operations, coordination, and science among distributed spacecraft necessitates functionality in navigation, communications, and control that leverage complex interactions among spacecrafts and between spacecrafts and the operating environment. Therefore, a need exists for a system that addresses these functions in an integrated, modular manner and that provides a structured approach to distributed spacecraft system design and implementation to effectively realize the advantages of such a system.
It is, therefore, an object of the present invention to provide a system that enables spacecrafts within in a distributed spacecraft system to communicate science and coordination information to determine relative position, velocity and time for command and control operations, and to operate in a coordinated manner to achieve common mission goals (e.g., interferometry, co-observation, implementing a synthetic sensing aperture, multipoint observation, etc.).
The above and other objects are achieved by providing an integrated navigation and communication system contained within a spacecraft, that enables control operations and science operations in a distributed spacecraft system including multiple spacecraft, comprising: a stackable connector utilized as a system bus; at least one processor card; at least one Global Positioning System (GPS) receiver card; at least one crosslink receiver card for receiving signals from other spacecraft in the distributed spacecraft system; and at least one crosslink transmitter card for transmitting signals to the other spacecraft in the distributed spacecraft system; wherein the at least one processor card, the at least one GPS receiver card, the at least one crosslink receiver card, and the at least one crosslink transmitter card are in communication with each other by each being connected to the stackable connector.